The present invention relates to a frictional torque hinge. More specifically, the present invention relates to a frictional element, or multiple frictional elements, radially compressed on a shaft, over which a housing is formed.
Frictional hinge devices are known in the art to support objects at selected angular positions relative to a main body. One type of friction hinge is a spring hinge which utilizes a helical spring wrapped around a shaft. In a relaxed state, the spring has an inner diameter less than the outer diameter of the shaft to frictionally engage the shaft so that the spring and shaft will tend to rotate together. In use, the shaft is connected to a rotatable body. As the body and the shaft are rotated, one of the spring ends or xe2x80x9ctoesxe2x80x9d is oriented to contact a stop, which is typically part of a stationary support. The engagement of the spring toe with the stop will cause the spring to slip relative to the shaft, rather than rotate with the shaft. This will generate torque. Such a spring hinge can be designed to provide a fairly constant torque or resistance to rotation throughout its range of motion.
Another type of friction hinge device is a wrap hinge with a shaft and an enclosure formed around the spring and shaft such that it encloses the shaft and spring. The spring is frictionally engaged with the shaft and therefore tends to rotate with the shaft. The enclosure surrounding the shaft, however has direct surface contact with the outer surface of the spring and prevents the spring from rotating relative to the enclosure. Thus, when the shaft is rotated relative to the enclosure, the friction between the shaft and the spring provides nearly constant torque or resistance to rotational movement throughout the range of motion of the shaft. Such a wrap spring device is disclosed in U.S. Pat. No. 5,542,505.
Another type of friction hinge device includes a shaft with a plurality of clips mounted on the shaft. Each clip has a connection portion projecting from the exterior surface. This connection portion engages a housing. Consequently, when the shaft is rotated relative to the housing, the clips are prevented from rotation via the engagement of the connection portion with the housing. The friction between the clips and the shaft upon their relative rotation provides a fairly constant torque or resistance to rotation throughout the range of motion. Such an housing is constructed separately from the clips. Great care must be taken to ensure that the housing properly engages the connection portion of the clips. Precision in the dimensions of these parts is very important.
Each of these known hinges, while providing certain advantages, also have limitations. A hinge that requires less expensive tooling in construction, requires less precision of parts in construction, that is water resistant, that provides a configuration for substantially containing lubricant, that has no moving parts in a mold during its formation, and after its formation, that has greater flexibility of hinge geometry, that allows for smaller overall size, or provides various combinations of these benefits, would be an improvement over the art of record.
The present invention is a friction torque hinge and method for making the same. The friction torque hinge in accordance with the present invention has a rotatable shaft, one or more frictional elements, and a housing. Each frictional element has an outer edge and an aperture that receives the shaft. The frictional elements are mounted on and frictionally engage the shaft.
In one embodiment, at least some of the frictional elements include a notch that is inside the outer edge of the frictional element. The housing substantially surrounds the plurality of frictional elements and the shaft, and it substantially fills the notches of the frictional elements.
The torque friction hinge of the present invention is formed by mounting a plurality of frictional elements on a shaft such that they are frictionally engaged therewith. The shaft and clips are then placed in a mold with a cavity for receiving them. Flowable material is then injected into the mold such that the material substantially surrounds the frictional elements. The flowable material then hardens into a housing that substantially contains the frictional elements.